dojo.coords(): wrong x/y when ancestor has border and style.overflow != visible (FF2)

[bill]

See attached test case. On FF2, dojo.coords(node) returns the wrong result if the node's parent (or probably any ancestor) has a border, and visibility=="hidden", "auto", or "scroll". The border's width is not taken into account.

This causes drop downs to position incorrectly, see #6787.

Since the bug is only with FF2 (it's a FF bug, not a bug in our code), I think we can mark this as won't fix, but leaving here for a record (and in case some one wants to fix it).

[bill]

test case for dojo.coords() bug (put in dijit/tests/layout)

[bill]

test case for underlying FF2 bug